In motor vehicle engineering, “brake-by-wire” braking systems are becoming ever more widespread. Such braking systems often include not only a master brake cylinder which can be actuated by the vehicle driver but also an electrically controllable pressure supply device, by means of which the wheel brakes are actuated in the “brake-by-wire” operating mode, either directly or via the master brake cylinder. In order to convey a pleasant pedal sensation to the vehicle driver in the “brake-by-wire” operating mode, the braking systems usually include a brake pedal sensation simulation device which is operatively connected, for example, to the master brake cylinder. In order to actuate the braking system, a setpoint value transmitter is provided which evaluates, for example, the electrical signals of one or more sensors for sensing the driver's braking request (actuation request), in order to determine a setpoint value for controlling the pressure supply device. In these braking systems, the pressure supply device can, however, also be actuated on the basis of electronic signals without active engagement by the driver. These electronic signals can be output, for example, by an electronic stability program (ESC) or an adaptive cruise control system (ACC), with the result that the setpoint value transmitter determines a setpoint value for controlling the pressure supply device on the basis of these signals.
International Patent Application WO 2008/025797 A1 discloses a braking system in which it is proposed that the pressure medium which is required for electrically controlling the pressure applied in an intermediate space used for actuating the master brake cylinder be kept available in a pressureless state in the pressure supply device and placed under relatively high pressure when necessary, in order to be able to dispense with the buffering of hydraulic actuation energy which is costly and energetically disadvantageous. The pressure supply device is for this purpose formed by a cylinder-piston arrangement, the piston of which can be actuated by an electromechanical actuator. A method for controlling the braking system, in particular the pressure supply device, is not described.
DE 10 2011 076 675 A1 describes a method for controlling an electrohydraulic braking system for motor vehicles having an electronically controllable pressure supply device which is connected to hydraulically actuable wheel brakes. The pressure supply device includes a cylinder-piston arrangement with a hydraulic pressure chamber, the piston of which can be displaced relative to a position of rest by an electromechanical actuator. For the purpose of control, an actual pressure value and a setpoint pressure value are determined and are fed to a controller device as input variables. The cylinder-piston arrangement is controlled by the controller device in such a way that the setpoint pressure value in the hydraulic pressure chamber is adjusted by displacing the piston.
The object of the present invention is to make available a method for controlling a braking system for motor vehicles and a corresponding control device and braking system which permit a dynamic brake pressure buildup at low or medium setpoint pressure values.
This object is achieved according to the invention by means of a method, a control device and a braking system as described herein.